This invention relates to the manufacturer of printheads used in fluid-jet printers, and more specifically to a fluid-jet printhead used in a fluid-jet print cartridge having improved dimensional control and improved step coverage.
One type of fluid-jet printing system uses a piezoelectric transducer to produce a pressure pulse that expels a droplet of fluid from a nozzle. A second type of fluid-jet printing system uses thermal energy to produce a vapor bubble in a fluid-filled chamber that expels a droplet of fluid. The second type is referred to as thermal fluid-jet or bubble jet printing systems.
Conventional thermal fluid-jet printers include a print cartridge in which small droplets of fluid are formed and ejected towards a printing medium. Such print cartridges include fluid-jet printheads with orifice structures having very small nozzles through which the fluid droplets are ejected. Adjacent to the nozzles inside the fluid-jet printhead are fluid chambers, where fluid is stored prior to ejection. Fluid is delivered to fluid chambers through fluid channels that are in fluid communication with a fluid supply. The fluid supply may be, for example, contained in a reservoir part of the print cartridge.
Ejection of a fluid droplet, such as ink, through a nozzle may be accomplished by quickly heating a volume of fluid within the adjacent fluid chamber. The rapid expansion of fluid vapor forces a drop of fluid through the nozzle in the orifice structure. This process is commonly known as xe2x80x9cfiring.xe2x80x9d The fluid in the chamber may be heated with a transducer, such as a resistor, that is disposed and aligned adjacent to the nozzle.
In conventional thermal fluid-jet printhead devices, such as ink-jet cartridges, thin film resistors are used as heating elements. In such thin film devices, the resistive heating material is typically deposited on a thermally and electrically insulating substrate. A conductive layer is then deposited over the resistive material. The individual heater element (i.e., resistor) is dimensionally defined by conductive trace patterns that are lithographically formed through numerous steps including conventionally masking, ultraviolet exposure, and etching techniques on the conductive and resistive layers. More specifically, the critical width dimension of an individual resistor is controlled by a dry etch process. For example, an ion assisted plasma etch process is used to etch portions of the conductive and resistive layers not protected by a photoresist mask. The width of the remaining conductive thin film stack (of conductive and resistive layers) defines the final width of the resistor. The resistive width is defined as the width of the exposed resistive layer between the vertical walls of the conductive layer. Conversely, the critical length dimension of an individual resistor is controlled by a subsequent wet etch process. A wet etch process is used to produce a resistor having sloped walls on the conductive layer defining the resistor length. The sloped walls of the conductive layer permit step coverage of later fabricated layers.
As discussed above, conventional thermal fluid-jet printhead devices require both dry etch and wet etch processes. The dry etch process determines the width dimension of an individual resistor, while the wet etch process defines both the length dimension and the necessary sloped walls commencing from the individual resistor. As is well known in the art, each process requires numerous steps, thereby increasing both the time to manufacture a printhead device and the cost of manufacturing a printhead device.
One or more passivation and cavitation layers are fabricated in a stepped fashion over the conductive and resistive layers and then selectively removed to create a via for electrical connection of a second conductive layer to the conductive traces. The second conductive layer is pattered to define a discrete conductive path from each trace to an exposed bonding pad remote from the resistor. The bonding pad facilitates connection with electrical contacts on the print cartridge. Activation signals are provided from the printer to the resistor via the electrical contacts.
Further, the wet etching process for defining the resistor length suffers from uniformity issues and can be highly dependent upon the chemistries used. The first conductive layer may be vulnerable to corrosion through pinholes and cracks in the passivation layers during subsequent wet etches.
The printhead substructure is overlaid with at least one orifice layer. Preferably, the at least one orifice layer is etched to define the shape of the desired firing fluid chamber within the at least one orifice layer. The fluid chamber is situated above, and aligned with, the resistor. The at least one orifice layer is preferably formed with a polymer coating or optionally made of an fluid barrier layer and an orifice plate. Other methods of forming the orifice layer(s) are know to those skilled in the art.
In direct drive thermal fluid-jet printer designs, the thin film device is selectively driven by electronics preferably integrated within the thermal electric integrated circuit part of the printhead substructure. The integrated circuit conducts electrical signals directly from the printer microprocessor to the resistor through conductive layers. The resistor increases in temperature and creates super-heated fluid bubbles for ejection of the fluid from the chamber through the nozzle. However, conventional thermal fluid-jet printhead devices can suffer from inconsistent and unreliable fluid drop sizes and inconsistent turn on energy required to fire a fluid droplet, if the resistor dimensions are not tightly controlled. Further, the stepped regions within the fluid chamber can affect drop trajectory and device reliability. The device reliability is affected by the bubble collapsing after the drop ejection thereby wearing down the stepped regions.
It is desirous to fabricate a fluid-jet printhead capable of producing fluid droplets having consistent and reliable fluid drop sizes and less susceptible to corrosion. In addition, it is desirous to fabricate a fluid-jet printhead having a consistent turn on energy (TOE) required to fire a fluid droplet, thereby providing greater control of the size of the fluid drops.
A fluid-jet printhead has a substrate on which at least one layer defining a fluid chamber for ejecting fluid is applied. The printhead includes an elevation layer disposed on the substrate and aligned with the fluid chamber. The printhead also includes a resistive layer disposed between the elevation layer and the substrate wherein the resistive layer has a smooth planer surface interfacing with the fluid chamber.
The present invention provides numerous advantages over conventional thin film printheads. First, the present invention provides a structure capable of firing a fluid droplet in a direction substantially perpendicular (normal or orthogonal) to a plane defined by the formed resistive element and ejection surface of the printhead. Second, the dimensions and planarity of the resistive material layer are more precisely controlled, which reduces the variation in the turn on energy required to fire a fluid droplet. Third, the size of a fluid droplet is better controlled due to less variation in resistor size. Fourth, the corrosion resistance and electro-migration resistance of the conductive layers are improved inherently by the design.